Sample of mixing middleware

apirouter.js

var router = require('koa-router')({prefix: '/api'});  // << important

router.get('/something', function *(next ){
  this.body = yield getSomething()
});

router.get('/somewhere', function *(next ){
  this.body = yield someWhere()
});

//... more like above, probably

module.exports = router

router.js

 /* /app/router.js */

"use strict;"

var serve = require('koa-static')
var WEBROOT= '/public'
var router = require('koa-router')();

// home redirect
router.redirect('/', '/index.html')

// Serve html  static files
router.get('/index.html', serve(WEBROOT+'/'))
router.get('/info.html', serve(WEBROOT+'/'))

// complex, probably render engine based pages
router.get('/complex.html', fucnhtion *(next){
  // your own bussines here
  this.body = yield this.render('complex');
})
// -- more like previous, probably

// nest the api router at the end
var apiRouter = require(appRoot+'/app/apirouter')
router.use(apiRouter.routes() )
router.use(apiRouter.allowedMethods() )

module.exports = router

server.js

   "use strict;"
var path = require('path');
var http = require('http')
var rewrite = require('koa-rewrite')
var serve = require('koa-static')
var views = require('koa-view')
var WEBROOT= '/public'
var ASSETS = WEEBROOT+'/assets'

var app ={},
    server = {},
    port = 3000;
function  start(){
    app = require('koa')()
    server = http.createServer(this.app.callback())

    // rewriting
    app.use(rewrite('/js/*', ASSETS+'/js/$1'))
    
    // static assets
    app.use(serve(ASSETS))
    
    // insert your view engine before the routes
    app.use(views('./views'))
    
    // routes
    var mainRouter =  require('/app/router')
    app.use( mainRouter.routes())
    app.use( mainRouter.allowedMethods())

}